Java计算器堆栈
所以我的任务是使用堆栈数据结构来设计一个简单的GUI计算器来执行加法,减法,乘法和除法。计算器窗口应至少有两个面板 - 一个用于显示,另一个用于按钮(0 - 9,。,+, - ,X,/,=,C)。输入表达式后,将显示其后缀或前缀,然后显示结果。Java计算器堆栈
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.util.Stack;
public class JCalculator implements ActionListener {
JFrame jfrm;
JFrame jfrm2;
JTextField txt;
JLabel results;
String str = "";
Stack operands = new Stack();
char[] a = new char[0];
int used = 0;
JCalculator(){
jfrm = new JFrame("JCalc");
jfrm.getContentPane().setLayout(new GridLayout(0,1));
jfrm.setSize(210,210);
results = new JLabel("",SwingConstants.RIGHT);
jfrm.getContentPane().add(results);
jfrm.setLocation(400,300);
jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton[] calbut= new JButton[14];
String []but = {"7","8","9","/","4","5","6","*","1","2","3","-","0","C"
};
JButton equal = new JButton("=");
JButton add = new JButton("+");
JPanel jbutton = new JPanel();
jbutton.setLayout(new GridLayout(4,3));
for(int i=0; i< but.length;i++){
jbutton.add(calbut[i] = new JButton(but[i]));
calbut[i].addActionListener(this);
}
jbutton.add(equal);
jbutton.add(add);
equal.addActionListener(this);
add.addActionListener(this);
jfrm.getContentPane().add(jbutton);
jfrm.setVisible(true);
}
public void actionPerformed(ActionEvent ae){
char[] a = new char[0];
int used = 0;
if(used == a.length){
char[] newa= new char[a.length + 1];
for(int i = 0; i <used; i++) newa[i]= a[i];
a= newa;
}
if(ae.getActionCommand().equals("1")){
str = results.getText();
results.setText(str + "1");
operands.push(1);
}
if(ae.getActionCommand().equals("2")){
str = results.getText();
results.setText(str + "2");
operands.push(2);
}
if(ae.getActionCommand().equals("3")){
str = results.getText();
results.setText(str + "3");
operands.push(3);
}
if(ae.getActionCommand().equals("4")){
str = results.getText();
results.setText(str + "4");
operands.push(4);
}
if(ae.getActionCommand().equals("5")){
str = results.getText();
results.setText(str + "5");
operands.push(5);
}
if(ae.getActionCommand().equals("6")){
str = results.getText();
results.setText(str + "6");
operands.push(6);
}
if(ae.getActionCommand().equals("7")){
str = results.getText();
results.setText(str + "7");
operands.push(7);
}
if(ae.getActionCommand().equals("8")){
str = results.getText();
results.setText(str + "8");
operands.push(8);
}
if(ae.getActionCommand().equals("9")){
str = results.getText();
results.setText(str + "9");
operands.push(9);
}
if (ae.getActionCommand().equals("0")) {
str = results.getText();
results.setText(str + "0");
operands.push(0);
}
if(ae.getActionCommand().equals("+")){
str = results.getText();
double operand = Double.parseDouble(str);
operands.push(operand);
results.setText("");
a[used]= '+';
used++;
}
if(ae.getActionCommand().equals("-")){
str = results.getText();
double operand = Double.parseDouble(str);
operands.push(operand);
results.setText("");
a[used]= '+';
used++;
}
if(ae.getActionCommand().equals("/")){
str = results.getText();
double operand = Double.parseDouble(str);
operands.push(operand);
results.setText("");
a[used]= '+';
used++;
}
if(ae.getActionCommand().equals("*")){
str = results.getText();
double operand = Double.parseDouble(str);
operands.push(operand);
results.setText("");
a[used]= '*';
used++;
}
if(ae.getActionCommand().equals("=")){
for(int i = 0; i< used; i++){
performBinaryOp(a[i]);
}
str = String.valueOf(operands.pop());
results.setText(str);
}
}
public void performBinaryOp(char nextOperation) {
double leftOperand, rightOperand;
Double result = new Double(0);
rightOperand = (Double) operands.pop();
leftOperand = (Double) operands.pop();
switch (nextOperation) {
case '+':
result = new Double(leftOperand + rightOperand);
break;
case '-':
result = new Double(leftOperand - rightOperand);
break;
case '*':
result = new Double(leftOperand * rightOperand);
break;
case '/':
result = new Double(leftOperand/rightOperand);
break;
}
operands.push(result);
}
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable() {
public void run() {
new JCalculator();
}
});
}
}
,我碰上是当按下按钮等于,例如按下2 + 3 =它返回第一个值2.0误差然后我收到一条错误消息:
Exception in thread "AWT-EventQueue-0" java.util.EmptyStackException
at java.util.Stack.peek(Unknown Source)
at java.util.Stack.pop(Unknown Source)
at JCalculator.actionPerformed(JCalculator.java:152)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
我很确定我的问题是我有一个空的堆栈,但我不知道代码错在哪里或如何解决它,所以任何帮助将不胜感激。
我建议您将Swing和UI放在一边,直到您的计算器正常工作。创建一个单独的Calculator类,可以接受文本字符串并对它们进行评估。一旦你有这个工作,然后添加一个用户界面。
是的,你已经有了一个栈的问题,就如同例外告诉你:
at JCalculator.actionPerformed(JCalculator.java:152)
在文本编辑器打开你的JCalculator,把行数显示,并转到行152这是你的问题在哪里。
我不愿意通读您发布的代码,但我会说与调试器快速旋转应该很快就清除它。
好吧谢谢我会看看在它并尝试你的建议,再次感谢 – 2012-04-10 01:46:11
你actionPerformed()
方法shadows一些类变量;请注意,您已重新声明char [] a
和int used
,因此您的代码几乎肯定不会按照您的预期运行。我没有遵循这个逻辑结论。
public class JCalculator implements ActionListener {
JFrame jfrm;
JFrame jfrm2;
JTextField txt;
JLabel results;
String str = "";
Stack operands = new Stack();
char[] a = new char[0];
int used = 0;
/* ... */
public void actionPerformed(ActionEvent ae){
char[] a = new char[0];
int used = 0;
if(used == a.length){
char[] newa= new char[a.length + 1];
for(int i = 0; i <used; i++) newa[i]= a[i];
a= newa;
}
这部分代码让我觉得,你不接受两个数字:
if(ae.getActionCommand().equals("1")){
str = results.getText();
results.setText(str + "1");
operands.push(1);
}
的operands.push(1)
可能须推动数正在生成,而不仅仅是最最近的数字。 (当然,如果你的意图是仅支持单位数字,这看起来没问题。)
我建议试图用单个函数替换那些十个小的if
语句。在这里花时间弄清楚一个函数是非常值得的,它将大大简化将来代码的维护,并且技巧是至关重要的。 (我想建议你考虑你的整齐JButton
初始化早些时候 - 并尝试在你的替换功能使用数组它可能不是最好的,但它应该是好的。)
if(ae.getActionCommand().equals("/")){
str = results.getText();
double operand = Double.parseDouble(str);
operands.push(operand);
results.setText("");
a[used]= '+';
used++;
}
你会注意到你的a[used]
被分配了错误的符号。一旦你修复了你的变量shadowing问题,这个将成为一个问题。尝试找出一种方法,用另一种单一功能取代这四个if
块 - 再一次,当向计算器添加新操作符时,它会使这种错误变得更加困难,并且会修复运算符应用代码中的错误更容易,因为你只需要修复一个位置的错误。
我不能强调足够强调将代码分解成“最小合理”功能的有用程度。您可以测试小函数比大函数更容易,并且将来您的代码将更易于阅读。
感谢您的有用的提示和想法,我一定会尝试修复我的代码。 – 2012-04-10 01:44:53
我的荣幸,快乐的节目。 :) – sarnold 2012-04-10 01:46:38
您是否希望获得固定的整个应用程序或解决当前错误?如果您试图解决当前问题,请在从该堆栈弹出之前添加一行以检查操作数是否为空。 基本上更改处理程序为 “=” 为: '如果(ae.getActionCommand()等于( “=”)。){ 如果(operands.isEmpty()) \t回报;' – 2012-04-10 01:31:13
我希望获得整个应用程序修复,你是说我有更多的错误? :/ – 2012-04-10 01:32:57
没有错误本身,但计算器不会真的“计算” – 2012-04-10 01:34:11